If you have a new account but are having problems posting or verifying your account, please email Niamh on [email protected] for help. Thanks :)
New AMA with a US police officer (he's back!). You can ask your questions here

Do all dinosaurs form a clade (or, are birds fish)?

  • 23-01-2021 6:55am
    Registered Users Posts: 7,008 ✭✭✭ Quantum Erasure

    Theres a podcast by the researchers on QI called There's No Such Thing as a Fish, which i recently heard of, so i googled and found this
    A clade is a group that includes all the descendents of a common ancestor and that ancestor, and all the different organisms that we think of as fish don't form a clade. Look at the phylogeny here. Almost everything you see on this phylogeny is a fish — with one exception. The lobe-finned lineage (technically called the Sarcopterygii) includes both the lobe-finned fish and [all] four-legged vertebrates


    Then i googled a bit on dinosaurs and came across this
    In 1888 the British paleontologist Harry Govier Seeley argued that Owen’s Dinosauria didn’t make up a natural group, but instead was a mash of what he saw as two very different groups of ancient reptiles. Seeley instead separated these two groups on the basis of their hip shape. There was the Saurischia, which he defined by its roughly lizard-like kind of hip, and included the sauropod and theropod dinosaurs. And then there were the Ornithischia, which had a more bird-like kind of hip, and comprised armored dinosaurs, horned dinosaurs, duckbill dinosaurs and their relatives. (The irony being that we now know “bird-hipped” dinosaurs are not closely related to birds at all. Birds are technically saurischian dinosaurs with highly-modified hips.)

    I've always had a bit of aa idological problem accepting that birds are dinosaurs, seems to me that if we are to accept them as dinos, we should accept them as fish aswell...


  • Moderators, Science, Health & Environment Moderators Posts: 5,279 Mod ✭✭✭✭ Adam Khor

    Well, it really doesn´t make much sense to put, say, Tyrannosaurus in one group along with the likes of Triceratops and Brontosaurus, and birds in another separate group, if you consider that Tyrannosaurus is much more closely related to birds (any bird) than it is to the other two. If you were to separate them you'd be creating an arbitrary, artificial group pretty much at random- it wouldn´t have much taxonomical value.

    So the question would be, should we move Tyrannosaurus to the bird group? But then maybe you'd have to move all other theropods (allosaurs, carcharodontosaurs, spinosaurs, ceratosaurs, you name it) into the bird group too, because they are more closely related to birds than to say, sauropods, so it's weird to keep them apart.

    And then why stop there? Sauropods, going by the Saurischia/Ornithischia classification, would also be closer to birds than to the other dinosaurs. So do we move them into birds with the theropods?

    I think it makes more sense to simply include birds as a subset of theropod dinosaurs- they don´t stop being birds, and they also don´t stop being dinosaurs because of it.

    (And yes, that would indeed make birds/dinosaurs AND us fish, too!)